The invention relates to an autofocus camera for recording television, photographic or cinematographic images. In the camera, an image of a scene to be recorded is formed on an electronic image sensor via an optical lens system. An aperture device is provided in the lens system for partly blocking the optical path in the lens system. This partial blocking action is produced at first and second portions of the optical path. The two portions are situated at substantially opposite positions on either side of a central axis of the optical path.
The camera comprises a signal comparison circuit for comparing the signals supplied by the sensor generated in first and second partial blocking periods during blocking of the first and second optical path portions, respectively. The focusing device provides substantially optimum focusing depending on the result of the comparison.
Such a camera is disclosed in U.S. Pat. No. 4,381,523. By partially blocking the optical path, two images are obtained via different portions of the optical lens system. When focusing is optimum, the two images are optimally in registration. A nonoptimum focusing results in images which are shifted relative to each other, the direction of the shift depending on whether there is overfocusing or underfocusing. During the signal comparison operation, the fact that the two images are shifted relative to each other is shown by a nonoptimum signal correlation. To obtain an optimum signal correlation, the focusing position is adjusted in the correct direction.
The described camera comprises a separate sensor for effecting the automatic focusing operation, or a single sensor having a specially dedicated portion therefor.